$ { \left[\begin{array}{r}{1} \\ {-2} \\ {1}\end{array}\right]-\left[\begin{array}{r}{2} \\ {0} \\ {-1}\end{array}\right] = {?} } $
Explanation: To find the difference of two matrices, subtract the corresponding items between each matrix. ${\left[\begin{array}{r}{1}-{2} \\ {-2}-{0} \\ {1}-{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-1} \\ {-2} \\ {2}\end{array}\right]}$